Re: [PATCH 3/4] zsmalloc use zs_handle instead of void *

[Nitin Gupta]

On 5/10/12 11:19 AM, Greg Kroah-Hartman wrote:
> On Thu, May 10, 2012 at 10:11:27AM -0500, Seth Jennings wrote:
> > On 05/10/2012 09:47 AM, Nitin Gupta wrote:
> >
> > > On 5/10/12 10:02 AM, Konrad Rzeszutek Wilk wrote:
> > > > struct zs {
> > > >      void *ptr;
> > > > };
> > > >
> > > > And pass that structure around?
> > >
> > > A minor problem is that we store this handle value in a radix tree node.
> > > If we wrap it as a struct, then we will not be able to store it directly
> > > in the node -- the node will have to point to a 'struct zs'. This will
> > > unnecessarily waste sizeof(void *) for every object stored.
> >
> >
> > I don't think so. You can use the fact that for a struct zs var,&var
> > and&var->ptr are the same.
> >
> > For the structure above:
> >
> > void * zs_to_void(struct zs *p) { return p->ptr; }
> > struct zs * void_to_zs(void *p) { return (struct zs *)p; }
>
> Do like what the rest of the kernel does and pass around *ptr and use
> container_of to get 'struct zs'.  Yes, they resolve to the same pointer
> right now, but you shouldn't "expect" to to be the same.

I think we can just use unsigned long as zs handle type since all we 
have to do is tell the user that the returned value is not a pointer. 
This will be less pretty than a typedef but still better than a single 
entry struct + container_of stuff.

Thanks,
Nitin

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